This invention relates generally to apparatus for industrial processing of bulk solids, i.e., powders, granulations and other particulate solid materials, including mixtures of such materials comprising solids of differing compositions and sizes. More particularly, the invention relates to apparatus for transferring such solids from one container to another, for example from a blender or bin to a portable bin, drum or container for transfer to another location, or for storage.
Under certain circumstances, bulk solid transfer may result in degradation of the quality of the solids including aeration of the material and segregation, that is, demixing of blended mixtures, with the consequent loss of uniformity of the content in the receiving container. Moreover, when the solids comprise fine or pulverulent materials, dust may be generated with exposure hazards to persons in the vicinity, as well as cleaning and other maintenance difficulties.
An example of the foregoing problems arises in the pharmaceutical industry in the manufacture of solid dosage forms of blended ingredients such as tablets or capsules. Typically, the ingredients are blended by known means such as tumbling or recirculation, and are then required to be transferred from the blender to a portable bin or drum from which they are later discharged into a tablet press or other device. Typical industry practice is to mate the outlet of a blender to the inlet of a bin, or simply to put the opening of the bin under the blender without a fixed connection. In either case, as the bin is filled material falls through the air and dust is generated.
In other industries such as the filling of ships and the forming of stockpiles, structures are provided in the form of let-down chutes extending between the two containers. Typically, this involves a fabric tube with a conical bottom, the latter in some cases comprising a series of cones which stack together, to form a contained path for the falling material. As the pile forms the fixture is raised by pulling up on cables connected to the bottom cone. Apparatus of that type is generally unacceptable in the pharmaceutical industry for at least four reasons. First, in the pharmaceutical industry all equipment is often completely cleaned after each batch has been blended and transferred. In cleaning, hidden surfaces present a particular problem for acceptable maintenance. A second objection is that these methods require the use of cables to pull up the device. To be certain that no foreign material enters the powder or other bulk solids, cables including those of metal composition are not allowed to enter the receiving container, even if they remain attached to the let-down fixture. Thirdly, let-down fixtures generally take up significant head room, frequently unavailable in existing facilities. Fourthly, these devices allow free-fall of the material while the tube is being initially filled with the material.
A principal object of this invention is to provide means for transfer of bulk solids that eliminate the unconfined fall of the solids from the discharge opening of the upper container to the top of the pile in the lower container, thereby eliminating the generation of dust, aeration of the material and segregation of blends of particles having differing physical characteristics.
A second object of the invention is to provide let-down means that avoid contamination of the material in the receiving container.
A third object is to provide let-down means that may be easily cleaned and maintained in use.